The purpose of this project is to investigate the pathogenesis of recurrent aphthous stomatitis and to develop effective therapy. Immunological studies include HLA typing, which has shown an association with HLA types A2 and BW44 lymphocyte transformation, which is depressed, and assays for cytokines and macrophage suppression which are normal. Other studies are underway to examine polymorph function and T helper and T suppressor cell function as well as immunoglobulin production measured by Elisa. Clinical studies include gathering epidemological data on patients and hematological studies. Food allergy and trauma have been identified as initiating factors and the assessment of various drugs on double-blind basis including zinc sulphate and cimetidine are underway.